With the wrack in middle position, preheat the oven to 350°F (180°C). Line a baking sheet with a silicone mat or parchment paper.
In a bowl, combine the sesame seeds, yeast, lemon zest, lemon juice and oil. Spread out into a thin layer on the baking sheet.
Bake for 25 minutes, stirring occasionally, until the mixture is completely dry. Let cool completely.
Using a mortar and pestle, coarsely grind the coriander seeds, fennel seeds, peppercorns and red pepper flakes. Add the sumac, garlic powder, onion powder and cooled sesame mixture. The steak spice with keep for 1 month in an airtight container at room temperature.